Labyrinthic septum wave guide



May 14, 1963 c. D. LUNDEN LABYRINTHIC SEPTUM WAVE GUIDE Filed Feb. 27, 1961 INVENTOR CZAAENGE D. LUA/DlF/V REY Z United States Patent 3,090,020 LABYRINTHIC SEPTUM WAVE GUIDE Clarence D. Lunden, Tacoma, Wash, assignor to Boeing Airplane Company, Seattle, Wash, a corporation of Delaware Filed Feb. 27, 1961, Ser. No. 91,774 12 Claims. (Cl. 33395) This invention relates to improvements in .wave guide configurations and structures, and more particularly concerns wave guides for frequencies in the range between about 200* and 2000 megacycles per second, although it is not necessarily limited to that range. The invention is herein illustratively described by reference to the presently preferred embodiments thereof; however, it will be recognized that certain modifications and changes therein with respect to details may be made without departing from the essential features involved.

Conventional wave guide forms used for frequencies in the range mentioned above are large, bulky and expensive. Moreover, conventional wave guides, particularly rectangular guides, of such large size have a tendency to distort when pressurized, unless the walls are unusually heavy or reinforced. Long runs of conventional wave guides introduce phase dispersion as between frequency components, thereby limiting permissible modulation basebandwidth.

On the other hand, it is also recognized that coaxial transmission lines are not altogether suitable at frequencies above about 500 megacycles per second, and that the use of insulation beads in these lines imposes peak power limitations due to breakdown of the insulation material. Furthermore, the presence of these insulation beads limits average power capacity because of the limited ability of the insulation to withstand heating. Vibration sensitivity and structural rigidity are also problems in coaxial lines, as is the limitation on safe ambient operating temperature.

Septate guides and coaxial lines have been proposed heretofore. These generally comprise an outer shell and a flat septum or divider projecting inwardly from one side of the shell along the midplane. In the case of a coaxial septum line, the inner and outer conductors are maintained in spaced relationship by the septum, the inner conductor comprising a bead on the projecting end of the septum. These devices have serious peak power limitations, however, because of the tendency for breakdown to occur due to the high electric field intensity which develops at the end of the septum. These breakdowns occur because the septum is located at the point of maxi mum electric field intensity in the case of a guide or line operated in the fundamental transverse electric field (TE mode. Furthermore, while some advantage is gained by use of the conventional septum construction in terms of the ability of such a guide to handle longer wave lengths for a given size of the outer shell, this gain is largely offset by the peak power limitation.

A broad object of the present invention is to provide a novel and improved wave guide which overcomes the aforementioned and related limitations or previous guides and coaxial lines.

With the improved wave guide configurations, of which there may be various specific forms within the broad concepts of the invention, the conductive interior surfaces are so formed and so spaced in relation to each other that the efiective width of the [guide in a direction transverse to the voltage vector is large, hence the cut-off wavelength is greatly increased, in comparison with conventional guides of a given exterior size. Moreover, the opposing surfaces are relatively flat or only gently curved in the region of maximum electric field intensity, so that ammo Patented May 14, 1963 "ice breakdown voltage is high. No insulating supports are required. Thus, lightweight compact systems capable of propagating energy at long wave lengths and at maximum peak and average power levels are attainable. By appropriate design, losses may be held at a minimum. While losses are not as small as with a conventional guide having the same cut-off frequency, such as a guide of circular or rectangular cross section, the losses are no greater than those incurred in beaded coaxial transmission lines, and are comparable with those incurred in septate guides, but without being subject to the other limitations described above.

Furthermore, long runs of wave guide using any of these novel guide configurations may be employed without the phase dispersion problem encountered in conventional guides. Since their outer shell is or may be of relatively small size and may be made circular if desired, these guides may easily be designed to withstand heavy external pressures and may be readily pressurized without physical distortion.

The improved guides may be manufactured in extruded forms or may be fabricated from extruded sections or in accordance with any other convenient or suitable manufacturing technique.

Basically, the improved guides comprise an internally conductive outer shell within which is mounted in spaced relation an open-sided inner shell or channel having conductive interior and exterior surfaces and joined to the outer shell for positioning purposes as well as for partitioning purposes by a web or septum which bears a predetermined relation to the inner shell depending upon the particular configuration chosen. In the preferred configurations the outer shell and the tubular inner shell are of similar cross-sectional form, although the inner shell comprises only the major arc of that form, and the septum or supporting partition extends between the outer shell and the inner shell along a plane which bisects the opening in the side of-the inner shell so as to define, conjunctively with the outer shell, a labyrinthical propagation space which greatly increases the effective width of the Wave guide as to its cut-off wave length characteristic. This it does by efiectively utilizing the interior space within the inner shell. In such a configuration a symmetry is achieved in which the point of maximum electric field intensity is that which lies directly between the inner and outer shells on that side of the inner shell which is directed away from the supporting septum, and at this location the conductive surfaces presented by the two shells are gently curved and suited to Withstand high field intensities without breakdown.

In still another embodiment the tubular inner shell comprises a spiral configuration the outer extremity of which extends into contact with the outer shell to be supported by it.

In another embodiment a series of open-sided inner shells are mounted one within another on a supporting septum to form a labyrinth of increased depth.

These and other features, objects and advantages of the invention will become more fully evident from the following description thereof by reference to the accompanying drawings.

FIGURE 1 is a perspective view of the invention in its preferred form.

FIGURE 1A is a cross section showing a variation of the guide illsutrated in FIGURE 11.

FIGURE 2. is a similar view of a modification.

FIGURE 3 is a similar view of a third embodiment.

FIGURE 4 is a cross-sectional view of a fourth em bodiment; and FIGURE 5 is a cross-sectional view of still another embodiment.

Referring to FIGURE 1, the tubular outer shell 10 is chosen to be of circular cross section, although other tubular cross-sectional forms may also be used. The tubular inner shell 12, spaced within the outer shell, has an open side and represents the major arc of a tube preferably of a configuration similar to that of the outer tube but eccentrically offset in the sense away from that wall of the outer tube which is opposite the open side of the inner tube. The inner tubular shell 12 is supported by a septum or partition 14 which is contiguously joined to the outer shell and extends inwardly therefrom in an axial plane. This septum bisects the open side of the shell 12 and extends across the interior thereof to a transversely centered location on its opposite wall, to which it is contiguously joined. These parts may be extruded or otherwise formed and may be silver-brazed together in order to obtain the necessary electrical continuity at the joints. Preferably the edges of the inner shell have rounded enlarged beads 12a and 12b, respectively, which serve to minimize dielectric stress concentrations and thereby extend the upper limit of peak power handling capacity of the composite wave guide.

It will be observed that, because of the eccentricity of the shells relatively, the distance e separating the two shells at a location opposite from the septum 14 represents the maximum direct spacing between the shells in this preferred embodiment. Thus, when the wave guide is operated in its fundamental transverse electric mode, the voltage is maximum where the spacing is maximum, and the voltage components are Zero at the wave guide side extremities, namely, at points m and 12. Moreover, the inner shell surface has a large radius of curvature in those regions wherein the voltage approaches its maximum value, which it attains at the location of measurement e, and there is, therefore, minimum tendency for breakdown to occur. At the location of the beads 12a and 12b the voltages are low in comparison, so that even though the radii of curvature of the beads are small in comparison, the voltage breakdown tendency is not a problem. If desired, these beads may be enlarged by curling the edges of the inner shell 12 back upon themselves in order to further reduce the dielectric stresses at this location, and, if desired, to increase the effective width or depth of the reentrancies within the inner shell. This is illustrated in FIGURE 1A wherein an increased labyrinthical depth is attained by the described expedient, thereby further increasing the cut-off wave length of the composite guide.

In FIGURE 2 the effective propagation space width of a wave guide using the principles shown in FIGURE 1 is further increased by the expedient of mounting a smaller, second septum shell 16 within the shell 12, and with its opening directed oppositely from the opening in the shell .12. The shell 16 intersects and is supported by the septum or partition 14 at an intermediate location between the edges thereof connected to the outer shell 10 and the inner shell 12 in order to maintain the innermost shell 16 spaced generally within the shell .12. Preferably shell 16 is offset or eccentrically located within the intermediate shell 12, the offset being in a direction opposite the offset of shell 12 in relation to shell 10. The purpose of the offset is the same as before, namely, so that there will be a general progression of spacing between opposing conductive surfaces of the various shells from minimum spacing at the points of minimum voltage to maximum spacing at the point of maximum voltage existing between the surfaces.

In the further modification shown in FIGURE 3, the septum 14' is so curved in its cross-sectional outline, as is the internal surface 12'c of the inner shell 12', as to form a wave propagation space which has a progressively and gradually decreasing thickness as measured between the opposing surfaces on which the electric field vectors terminate. At the measurement point e, the point of maximum spacing, the design spacing is such that it will withstand the operating peak power levels required of the system. The spacing then drops off progressively in an approximately sinusoidal curve from that measurement location to the opposite extremities of the labyrinthical space, until it is zero or substantially zero at the extremities In and n.

In the further modification shown in FIGURE 4 a configuration similar to FIGURE 1 is employed, using generally rectangular inner and outer shells.

In the further modification shown in FIGURE 5, the outer shell 29 is of tubular form, whereas the inner shell 22 is of a spiral configuration. The outer extremity of this spiral extends into contact with the outer shell at a point 24 where the two intersect at an acute angle A and are joined together in electrically contiguous manner. It then curves progressively away from the outer shell to a location of maximum spacing between them, as indicated by the measurement line e, whereupon it preferably curves progressively away from the outer shell as the spiral surface 22 wraps back upon itself and in so doing forms an internal reentrant space which extends the effective width and cut-off wave length of the total propagation space within the guide. In this case the side extremities m and n are represented by the reentrant space extremity within the spiral configuration and by the reentrant space formed in the angularly disposed surfaces of the two shells at the point of intersection, 24.

These and other aspects of the invention will be evident to those skilled in the art based on the preferred embodiments thereof as disclosed in the above specification.

I claim as my invention:

1. A guide for electromagnetic wave energy propagation, said guide being of hollow tubular construction, the interior wave energy propagation cross section of which is defined by an enclosing outer wall to which is joined an internal partition structure including a base portion projecting inwardly from the outer wall, and an adjoining portion which, while remaining spaced from the outer wall, continues from the base portion back at least partially toward the juncture of the outer wall and base portion and in so doing generally reverses its direction of extent to define, within said partition structure, a reentrant propagation space which is contiguous to the propagation space defined between the outer wall and the base portion.

2. The guide defined in claim 1, wherein the partition portion base structure comprises a septum which projects from one side of the outer wall generally centrally across the guide and terminates short of the opposite side thereof, and the adjoining portion comprises elements projecting transversely from the septum in directions opposite from each other toward the respective intervening sides of the guide and thereupon turn toward the firstmentioned side, with the direct distance of separation between the partition structure and the outer wall being maximum at a location opposite the septum and decreasing progressively on either side of said location.

3. The guide defined in claim 2, wherein the outer wall comprises the interior surface of a round tubular form, and wherein said adjoining portion of the partition structure comprises in cross section a major arc of a second round tubular form, the transversely opposite ends of which are directed inwardly toward and terminate at locations spaced outwardly from the respective sides of the septum.

4. The guide defined in claim 3, and. wherein the partition structure further comprises the major arc portion of a round tubular form smaller than the second round tubular form and mounted at an intermediate level on the septum with its open side directed into the reentrant space defined within the second tubular member, thereby to form a labyrinthical reentrant propagation space within the partition structure.

5. The guide defined in claim 1, wherein the internal partition structure comprises a curved septum which pr0- jects inwardly from the outer wall at an angle and which follows an inward spiral configuration.

6. A guide for electromagnetic wave energy propagation, said guide comprising an internally conductive tubular outer shell, a generally tubular internal shell spaced within said outer shell to form a propagation space therebetween, said internal shell having an open side and conductive interior and exterior surfaces, and a conductive partition interconnecting the shells to maintain the spacing therebetween, said partition extending into the interior of the internal shell and forming conjunctively therewith a reentrant propagation space continuous with the propagation space between the shells.

7. The guide defined in claim 6, wherein the internal tubular shell is substantially symmetrical about a medial longitudinal plane which bisects the shell opening, and the partition lies along such plane of bisection.

8. The guide defined in claim 6, wherein the internal tubular shell is substantially symmetrical about a medial longitudinal plane which bisects the shell opening, and the partition lies along such plane of bisection, and further wherein the internal shell is offset eccentrically in relation to the outer shell in the direction of the open side of the inner shell.

9. The guide defined in claim 6, wherein the internal shell is of generally spiral configuration and the partition comprises an extension of the outer end of the spiral to the point of connection thereof with the outer shell.

10. The guide defined in claim 6, wherein the internal shell is of generally spiral configuration and the partition comprises an extension of the outer end of the spiral to the point of connection thereof with the outer shell, the spacing between the shells increasing progressively from said point to a maximum in less than 360 of circumference of the outer shell and thereafter progressively decreasing to the reentrancy of the spiral.

11. A guide for electromagnetic wave energy propagation, said guide comprising an internally conductive outer shell, an internal open-sided internally and externally conductive channel spaced within said shell, and a partition projecting inwardly from said outer shell into directly adjoining relationship with the channel interior, said partition supportingly connected to said channel.

12. A septate wave guide comprising an internally con ductive outer shell and a conductive septate structure mounted within said shell and comprising an open-sided conductive channel and a conductive web projecting from the interior thereof on its open side to connect with the shell.

References Cited in the file of this patent UNITED STATES PATENTS 2,199,083 Schelkunofi Apr. 30, 1940 OTHER REFERENCES Barrow and Schalvitz: Hollow Pipes of Relatively Small Dimensions, AIEE Transactions, vol. 60, 1941. 

1. A GUIDE FOR ELECTROMAGNETIC WAVE ENERGY PROPAGATION, SAID GUIDE BEING OF HOLLOW TUBULAR CONSTRUCTION, THE INTERIOR WAVE ENERGY PROPAGATION CROSS SECTION OF WHICH IS DEFINED BY AN ENCLOSING OUTER WALL TO WHICH IS JOINED AN INTERNAL PARTITION STRUCTURE INCLUDING A BASE PORTION PROJECTING INWARDLY FROM THE OUTER WALL, AND AN ADJOINING PORTION WHICH, WHILE REMAINING SPACED FROM THE OUTER WALL, CONTINUES FROM THE BASE PORTION BACK AT LEAST PARTIALLY TOWARD THE JUNCTURE OF THE OUTER WALL AND BASE PORTION AND IN SO DOING GENERALLY REVERSES ITS DIRECTION OF EXTENT TO DEFINE, WITHIN SAID PARTITION STRUCTURE, A REENTRANT PROPAGATION SPACE WHICH IS CONTIGUOUS TO THE PROPAGATION SPACE DEFINED BETWEEN THE OUTER WALL AND THE BASE PORTION. 